Runtime error during django recursive template rendering

Question

I want to implement django recursive template rendering for getting users and their subordinates. However, I've got a ErrorRuntimeError at /admin/users/3 maximum recursion depth exceeded in instancecheck. I'm using django 1.9. The code is given below

The input is like that: [{name: 'user1@mail.com', id: 1, next: True}, {name: 'user2@mail.com', id: 2, next: True}, {name: 'user3@mail.com', id: 3, next: False}]

users_hierarchy.html

<ul>
{% for user in users %}
    <li>{{ user.name }}</li>
    {% if user.next %}
        <ul>
           {% include 'users/user_hierarchy.html' with data=user %}
        </ul>
    {% endif %}
{% endfor %}

I expect a html such as:

<ul>
<li>user1@mail.com
    <ul>
        <li>user2@mail.com
    <ul>
         <li>user3@mail.com</li>
    </ul>
        </li>  
    </ul>
</li>

What I am doing wrong?

You're passing the same user to the include, so the recursion can never return. You really need to pass the *next* user to the include; but there isn't a good way of getting it with the structure you have. — Daniel Roseman, Feb 08 '19 at 13:27
@DanielRoseman How could I pass the next user to the include? And what the better way to to organize my structure? — PolyMorph, Feb 08 '19 at 13:34
As I say, you can't do it in the template with the structure you have. Where does this data come from? Do you have control over the format? Ideally you want a structure like `{name: 'user1@mail.com', children: [{name: 'user2', children: [{name: 'user3'}]]}`. — Daniel Roseman, Feb 08 '19 at 13:39
The data is actually a RawQuerySet which is formed in for-loop by me to array of dictionaries, so I should change the form of input object and the code above will work? — PolyMorph, Feb 08 '19 at 14:21
Well, you would need to change the if statement to `if user.children` and the include to `with users=user.children`. — Daniel Roseman, Feb 08 '19 at 14:23

score 0 · Answer 1 · answered Feb 08 '19 at 13:28

I explain why you are in an infinite recursion

From djanto include template docs:

An included template is rendered within the context of the template that includes it.

That means you are iterating over users again and again:

<ul>
{% for user in users %}                 <-----(1)<------------------------<
    <li>{{ user.name }}</li>                                              |
    {% if user.next %}                                                    |
        <ul>                                                              |
           {% include 'users/user_hierarchy.html' with data=user %} --(2)->

At (1) you iterate over users. At first iteration you call the include (2). At this point you go to (1) (in nested included template) and start iteration again.

Thanks for the explanation, but how can I pass the next user within the same template? — PolyMorph, Feb 08 '19 at 13:37
What about to use django-mptt ? Take a look to this question: https://stackoverflow.com/questions/32044/how-can-i-render-a-tree-structure-recursive-using-a-django-template — dani herrera, Feb 08 '19 at 14:49

Runtime error during django recursive template rendering

1 Answers1